Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012
Cash flows from operating activities
Net loss	$ (25,899)		$ (14,039)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	3,537		1,379
Amortization of investment securities premium	938		(161)
Depreciation	40		88
Other	(10)		(252)
Changes in operating assets and liabilities:
Prepaid expenses, receivables and other current assets	(1,914)		274
Other assets	(120)		12
Accounts payable	(255)		(829)
Accrued expenses	2,531		1,182
Deferred revenue	(354)		(2,990)
Long-term liabilities	2
Net cash used in operating activities	(21,504)		(15,336)
Cash flows from investing activities
Purchases of investment securities	(186,756)		(15,609)
Maturities of investment securities	51,589		24,883
Purchases of property and equipment	(490)
Proceeds from sales of property and equipment	12		252
Net cash (used in) provided by investing activities	(135,645)		9,526
Cash flows from financing activities
Proceeds from issuance of common stock and warrants, net of issuance costs	111,053		6,967
Repayments of long-term debt			(28)
Net cash provided by financing activities	111,053		6,939
Effect of exchange rate changes on cash			(2)
Net (decrease) increase in cash and cash equivalents	(46,096)		1,127
Cash and cash equivalents
Beginning of period	57,899	[1]	6,889
End of period	11,803		8,016
Unrealized gain (loss) on investment securities	$ 80		$ (4)

[1] The condensed consolidated balance sheet at December 31, 2012 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by accounting principles generally accepted in the United States for complete financial statements.